Attempt to fix tests on Windows

Author: JukkaL

mypy/test/testdiff.py

@@ -34,7 +34,7 @@ def cases(cls) -> List[DataDrivenTestCase]:
     def run_case(self, testcase: DataDrivenTestCase) -> None:
         first_src = '\n'.join(testcase.input)
         files_dict = dict(testcase.files)
-        second_src = files_dict['tmp/next.py']
+        second_src = files_dict[os.path.join('tmp', 'next.py')]
 
         messages1, files1 = self.build(first_src)
         messages2, files2 = self.build(second_src)

mypy/test/testfinegrained.py

@@ -65,6 +65,8 @@ def run_case(self, testcase: DataDrivenTestCase) -> None:
                 modules.append(module)
 
             new_messages = update_build(manager, graph, deps, modules)
+            new_messages = [re.sub('^tmp' + re.escape(os.sep), '', message)
+                            for message in new_messages]
 
             a.append('==')
             a.extend(new_messages)

test-data/unit/fine-grained.test

@@ -168,7 +168,7 @@ def g(a: str) -> None:
     m.f('') # E
 [out]
 ==
-tmp/n.py:3: error: Too few arguments for "f"
+n.py:3: error: Too few arguments for "f"
 ==
-tmp/n.py:3: error: Argument 1 to "f" has incompatible type "str"; expected "int"
-tmp/m.py:3: error: Too few arguments for "g"
+n.py:3: error: Argument 1 to "f" has incompatible type "str"; expected "int"
+m.py:3: error: Too few arguments for "g"